U.S. patent application number 14/826997 was filed with the patent office on 2017-02-16 for method and system for high fuel vapor canister purge flow.
The applicant listed for this patent is Ford Global Technologies, LLC. Invention is credited to Ross Dykstra Pursifull.
Application Number | 20170045007 14/826997 |
Document ID | / |
Family ID | 57995399 |
Filed Date | 2017-02-16 |
United States Patent
Application |
20170045007 |
Kind Code |
A1 |
Pursifull; Ross Dykstra |
February 16, 2017 |
METHOD AND SYSTEM FOR HIGH FUEL VAPOR CANISTER PURGE FLOW
Abstract
Methods and systems are provided for managing fuel vapors in a
vehicle fuel system. In one example, a method includes commanding
or maintaining closed a vapor blocking valve during a purging
operation such that vapor flow is directed from a fuel tank to a
fresh air side of a vapor canister via a first restricted vapor
line, thereby enabling high purge flow rates and deep vapor
canister vacuum while avoiding fuel tank vacuum. In this way,
canister purge operation may be made more efficient, thereby
reducing hydrocarbon bleed emissions.
Inventors: |
Pursifull; Ross Dykstra;
(Dearborn, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Ford Global Technologies, LLC |
Dearborn |
MI |
US |
|
|
Family ID: |
57995399 |
Appl. No.: |
14/826997 |
Filed: |
August 14, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F02M 25/0854 20130101;
B60K 2015/03566 20130101; B60K 2015/03514 20130101; F02M 25/089
20130101; B60K 2015/03585 20130101; F02D 41/0032 20130101; F02D
41/042 20130101; B60K 15/03504 20130101; F02M 25/0836 20130101;
B60K 2015/03571 20130101; B60K 2015/03576 20130101 |
International
Class: |
F02D 41/00 20060101
F02D041/00; F02M 25/08 20060101 F02M025/08 |
Claims
1. A method for an engine, comprising: during a first condition,
closing a vacuum blocking valve (VBV) and directing vapor flow from
a fuel tank to a fresh air side of a vapor canister via a first
vapor line; and during a second condition, opening the VBV and
directing vapor flow from the fuel tank to a load/purge side of the
vapor canister via a second vapor line.
2. The method of claim 1, wherein directing vapor flow via the
first vapor line comprises directing vapor flow through a
restriction in the first vapor line.
3. The method of claim 2, wherein the restriction is comprised of
an orifice or a sonic choke.
4. The method of claim 2, wherein an overall vapor line bifurcates
upstream of the restriction into the first vapor line and second
vapor line, wherein the VBV is positioned in the second vapor
line.
5. The method of claim 1, wherein the first condition comprises
engine operation.
6. The method of claim 1, wherein the first vapor line does not
couple the fuel tank to the load/purge side of the vapor
canister.
7. The method of claim 1, wherein the first condition comprises a
canister purge event.
8. The method of claim 7, wherein the vapor canister is divided
into the fresh air side and the load/purge side by a partition
housed within the canister, the fresh air side further including a
vent line connected to fresh air via a canister vent valve (CVV),
the load/purge side connected to an intake manifold via one or more
canister purge valves (CPV), including a conventional CPV and/or a
low restriction CPV.
9. The method of claim 8, further comprising, during the canister
purge event, commanding open the low restriction CPV.
10. The method of claim 9, wherein the canister purge event
comprising an open low restriction CPV includes indicating whether
a fuel tank vacuum is greater than a threshold.
11. The method of claim 10, wherein indicating a fuel tank vacuum
greater than a threshold includes reducing purge flow rate such
that fuel tank vacuum is maintained below the threshold.
12. The method of claim 1, wherein the second condition includes a
refueling event.
13. A system for an engine, comprising: a fuel vapor canister
partitioned into a fresh air side and a load/purge side; a fuel
tank; and a bifurcated vapor line connecting the vapor canister to
the fuel tank, a first segment of the line comprising a restricted
orifice disposed within the first vapor line segment and connecting
to the vapor canister on the fresh air side, a second segment of
the vapor line comprising a vacuum blocking valve (VBV) disposed
within the second vapor line segment and connecting to the vapor
canister on the load/purge side.
14. The system of claim 13, further comprising: a canister vent
line coupled to the fuel vapor canister on the fresh air side; a
canister vent valve disposed within the canister vent line and
configured to selectively couple the vapor canister to fresh air; a
canister purge line coupled to the fuel vapor canister on the
load/purge side; and one or more canister purge valves (CPV)
disposed within the canister purge line and configured to
selectively couple the vapor canister to the an intake
manifold.
15. The system of claim 14, further comprising a controller holding
executable instructions stored in non-transitory memory, that when
executed, cause the controller to: during engine operation, command
the VBV closed; and during a refueling event, command the VBV
open.
16. The system of claim 15, wherein the one or more CPVs comprise a
first CPV and a second, low restriction CPV having a lower
restriction than the first CPV, and wherein the controller has
further instructions that when executed cause the controller to,
during a canister purge event, open the low restriction CPV and
maintain the VBV closed.
17. The system of claim 15, wherein when the VBV is open, the
second segment of the bifurcated vapor line has a smaller amount of
restriction than the first segment of the bifurcated vapor line
such that fuel vapor may flow from the fuel tank to the vapor
canister load side via the open VBV.
18. A system for an engine, comprising: a fuel vapor canister
partitioned into a fresh air side and a load/purge side; a fuel
tank; and a bifurcated vapor line connecting the vapor canister to
the fuel tank, a first segment of the vapor line comprising a
restricted orifice disposed within the first vapor line segment and
connecting to the vapor canister on the fresh air side, a second
segment of the vapor line comprising a vacuum blocking valve (VBV)
disposed within the second vapor line segment and connecting to the
vapor canister on the load/purge side; a canister vent line coupled
to the fuel vapor canister on the fresh air side; a canister vent
valve disposed within the canister vent line and configured to
selectively couple the vapor canister to fresh air; a canister
purge line coupled to the fuel vapor canister on the load/purge
side; a first canister purge valve (CPV) and second CPV each
configured to selectively couple the vapor canister to the an
intake manifold, the second CPV having a lower restriction than the
first CPV; and a controller holding executable instructions stored
in non-transitory memory, that when executed, cause the controller
to: responsive to a request to perform a canister purge with a
target flow rate above a threshold, maintain the VBV closed, open
the second CPV, and adjust a position of the first CPV to reach the
target flow rate, and responsive to a request to refuel the fuel
tank, open the VBV.
19. The system of claim 18, wherein the second segment of the fuel
vapor line has a cross-sectional area that is larger than a
cross-sectional area of the orifice, and wherein when open, the VBV
does not restrict the second segment of the fuel vapor line.
20. The system of claim 18, wherein the first segment of the vapor
line does not couple the fuel tank to the load/purge side of the
vapor canister, and wherein the second segment of the vapor line
does not couple the fuel tank to the fresh air side of the vapor
canister.
Description
FIELD
[0001] The present description relates generally to methods and
systems for controlling an evaporative emissions system to avoid
gasoline tank vacuum at high fuel vapor canister purge flow
rates.
BACKGROUND/SUMMARY
[0002] Vehicle emission control systems may be configured to store
fuel vapors from fuel tank refueling and diurnal engine operations
in a fuel vapor canister containing a suitable adsorbent, and then
purge the stored vapors during a subsequent engine operation. The
stored vapors may be routed to an engine intake for combustion,
further improving fuel economy.
[0003] In a typical canister purge operation, a canister purge
valve coupled between the engine intake and the fuel canister is
opened, allowing for intake manifold vacuum to be applied to the
fuel canister. On a boosted engine, that vacuum draw may be
supplied via an ejector during boosted operation. Simultaneously, a
canister vent valve coupled between the fuel canister and
atmosphere is opened, allowing for fresh air to enter the canister.
Further, in some examples a vapor blocking valve coupled between
the fuel tank and the fuel canister is closed to prevent the flow
of fuel vapors from the fuel tank to the engine. This configuration
facilitates desorption of stored fuel vapors from the adsorbent
material in the canister, regenerating the adsorbent material for
further fuel vapor adsorption.
[0004] However, reduced engine operation times in hybrid vehicles
can lead to insufficient purging of fuel vapors from the vehicle's
emission control system. For example, regions of adsorbent that see
relatively less air flow may retain relatively more hydrocarbons.
The residual hydrocarbons may desorb over a diurnal cycle, leading
to an increase in bleed emissions. Additionally, the capability of
the canister to trap additional vapors from the fuel tank greatly
depends upon how thoroughly the vapors are purged from the canister
when the vehicle was last operated. Accordingly, it is desirable to
purge the canister as much as possible while the engine is
running
[0005] As such, due to the shorter purge times available in hybrid
vehicles, purge operations tend to be more aggressive with higher
purge ramp rates (relative to corresponding non-hybrid vehicles).
In one example, U.S. Pat. No. 6,202,632 B1 teaches the use of a
controllable canister purge valve comprising a first connection to
the intake pipe of an engine and a second connection to a vapor
canister, the first and second connections interconnected via a
first controllable valve, as well as through a second valve
connected in parallel with the first. The second valve may comprise
a larger cross section than the first valve, such that greater flow
rates may be achieved via the opening of both the first and second
valves, in one example.
[0006] However, the inventors herein have recognized an issue with
the above approach. High purge rates can cause a significant
pressure drop across the canister, thus putting the fuel tank at a
vacuum. For example, during a purging operation a vacuum blocking
valve (VBV) may be closed to prevent flow of fuel vapors from the
fuel tank to the engine. In some examples the VBV may have a small
vapor path around it, intended to let fuel vapor escape slowly as
the tank pressurizes with heat gain and thus avoid pressure build.
Thus, with high purge rates, vacuum may develop in the fuel tank
via the vapor line around the VBV, even with the VBV closed. If the
purge rate is high enough, fuel tank vacuum may become high enough
to overcome the closing force of the fuel tank relief valve, thus
air and dirt particles may be drawn into the tank, and this flow
additionally does not serve to purge the canister.
[0007] Thus, the inventors herein have developed systems and
methods to at least partially address the above issues. In one
example, a method is provided, comprising during a first condition,
including an engine-on condition, closing a VBV and directing vapor
flow from a fuel tank to a fresh air side of a vapor canister via a
first vapor line, and during a second condition, including a
refueling event, opening the VBV and directing vapor flow from the
fuel tank to a load side of the vapor canister via a second vapor
line. In this way, VBV functionality is preserved while vacuum
generated at the fuel tank may be limited during conditions of high
canister purge flow rates. As one example, during a purging
operation a VBV may be maintained in a closed conformation. Because
the fuel tank is coupled to the vapor canister on the fresh air
side, not on the load/purge side, the vacuum imposed on the fuel
tank may be shallow as compared to a case in which the fuel tank is
coupled to the vapor canister on the load/purge side. As such, high
purge flow rates may be applied to purge the canister while low
fuel tank vacuum is maintained. In this way, vapor canister purging
may be made more efficient, thus reducing evaporative emissions.
The above advantages and other advantages, and features of the
present description will be readily apparent from the following
Detailed Description when taken alone or in connection with the
accompanying drawings.
[0008] It should be understood that the summary above is provided
to introduce in simplified form a selection of concepts that are
further described in the detailed description. It is not meant to
identify key or essential features of the claimed subject matter,
the scope of which is defined uniquely by the claims that follow
the detailed description. Furthermore, the claimed subject matter
is not limited to implementations that solve any disadvantages
noted above or in any part of this disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 shows a schematic depiction of an engine and an
associated fuel system, including a bifurcated vapor line coupling
the fuel tank to the vapor canister at both a fresh air side and a
load side.
[0010] FIG. 2 shows an example method for directing fuel vapors
from a fuel tank to a vapor canister via one or more paths,
depending on engine operating conditions.
[0011] FIG. 3 shows a timeline for performing a fuel vapor canister
purging operation.
DETAILED DESCRIPTION
[0012] The following detailed description relates to systems and
methods for managing evaporative emission system fuel vapors. More
specifically, the description relates to directing the flow of fuel
vapors from the fuel tank to the vapor canister via one or more of
two distinct paths, depending on engine operating conditions.
Directing the flow of fuel vapors via one or more of the two
distinct paths may be controlled by the open or closed state of a
vacuum blocking valve (VBV). The VBV may be housed between the fuel
tank and the vapor canister, as depicted in the engine system shown
in FIG. 1. A method for directing the flow of fuel vapors from the
fuel tank to the vapor canister via one or more of two distinct
flow paths, under varying engine operating conditions, is depicted
in FIG. 2. In one example, commanding or maintaining the VBV in a
closed state during a purging operation may enable a high canister
purge flow rate while minimizing the resulting vacuum imposed on
the fuel tank. A timeline for performing a high flow rate purge
operation incorporating these concepts is shown in FIG. 3.
[0013] FIG. 1 shows a schematic depiction of a hybrid vehicle
system 6 that can derive propulsion power from engine system 8
and/or an on-board energy storage device (not shown), such as a
battery system. An energy conversion device, such as a generator
(not shown), may be operated to absorb energy from vehicle motion
and/or engine operation, and then convert the absorbed energy to an
energy form suitable for storage by the energy storage device.
[0014] Engine system 8 may include an engine 10 having a plurality
of cylinders 30. Engine 10 includes an engine intake 23 and an
engine exhaust 25. Engine intake 23 includes an air intake throttle
62 fluidly coupled to the engine intake manifold 44 via an intake
passage 42. Air may enter intake passage 42 via air filter 52.
Engine exhaust 25 includes an exhaust manifold 48 leading to an
exhaust passage 35 that routes exhaust gas to the atmosphere.
Engine exhaust 25 may include one or more emission control devices
70 mounted in a close-coupled position. The one or more emission
control devices may include a three-way catalyst, lean NOx trap,
diesel particulate filter, oxidation catalyst, etc. It will be
appreciated that other components may be included in the engine
such as a variety of valves and sensors, as further elaborated in
herein.
[0015] In some embodiments, engine 10 maybe a boosted engine
wherein the engine intake includes a boosting device, such as a
turbocharger. When included, a turbocharger compressor may be
configured to draw in intake air at atmospheric air pressure and
boost it to a higher pressure. The turbocharger compressor may be
driven by the rotation of an exhaust turbine, coupled to the
compressor by a shaft, the turbine spun by the flow of exhaust
gases there-through. A boosted system may employ an ejector to
provide vacuum during boost. Similar to engine vacuum, this vacuum
draws fuel vapors into the engine combustion air.
[0016] Engine system 8 is coupled to a fuel system 18. Fuel system
18 includes a fuel tank 20 coupled to a fuel pump 21 and a fuel
vapor canister 22. During a fuel tank refueling event, fuel may be
pumped into the vehicle from an external source through refueling
door 108. Fuel tank 20 may hold a plurality of fuel blends,
including fuel with a range of alcohol concentrations, such as
various gasoline-ethanol blends, including E10, E85, gasoline,
etc., and combinations thereof. A fuel level sensor 101 located in
fuel tank 20 may provide an indication of the fuel level ("Fuel
Level Input") to controller 12. As depicted, fuel level sensor 101
may comprise a float connected to a variable resistor.
Alternatively, other types of fuel level sensors may be used.
[0017] Fuel pump 21 is configured to pressurize fuel delivered to
the injectors of engine 10, such as example injector 66. While only
a single injector 66 is shown, additional injectors are provided
for each cylinder. It will be appreciated that fuel system 18 may
be a return-less fuel system, a return fuel system, or various
other types of fuel system. Vapors generated in fuel tank 20 may be
routed to fuel vapor canister 22, via conduit 31, before being
purged to the engine intake 23.
[0018] Fuel vapor canister 22 is filled with an appropriate
adsorbent for temporarily trapping fuel vapors (including vaporized
hydrocarbons) generated during fuel tank refueling operations, as
well as diurnal vapors. In one example, the adsorbent used is
activated charcoal. When purging conditions are met, such as when
the canister is saturated (e.g., canister load is higher than a
threshold), hydrocarbons stored in fuel vapor canister 22 may be
purged to engine intake 23 by opening canister purge valve 112, by
opening canister purge valve 106, and opening canister vent valve
114. While a single canister 22 is shown, it will be appreciated
that fuel system 18 may include any number of canisters.
[0019] Canister 22 may include a buffer 103 (or buffer region),
each of the canister and the buffer comprising the adsorbent. As
shown, the volume of buffer 103 may be smaller than (e.g., a
fraction of) the volume of canister 22. The adsorbent in the buffer
103 may be same as, or different from, the adsorbent in the
canister (e.g., both may include charcoal). Buffer 103 may be
positioned within canister 22 such that during canister loading,
fuel tank vapors are first adsorbed within the buffer, and then
when the buffer is saturated, further fuel tank vapors are adsorbed
in the canister. In comparison, during canister purging, fuel
vapors are first desorbed from the canister (e.g., to a threshold
amount) before being desorbed from the buffer. In other words,
loading and unloading of the buffer is not linear with the loading
and unloading of the canister. As such, the effect of the canister
buffer is to dampen any fuel vapor concentration spikes flowing
from the fuel tank to the canister, thereby reducing any fuel vapor
spikes from going to the engine.
[0020] Canister 22 includes a vent 27 for routing gases out of the
canister 22 to the atmosphere when storing, or trapping, fuel
vapors from fuel tank 20. Vent 27 may also allow fresh air to be
drawn into fuel vapor canister 22 when purging stored fuel vapors
to engine intake 23 via purge line 28 and purge valve 112. While
this example shows vent 27 communicating with fresh, unheated air,
various modifications may also be used. Vent 27 may include a
canister vent valve 114 to adjust a flow of air and vapors between
canister 22 and the atmosphere. The canister vent valve may also be
used for diagnostic routines. The vent valve may be opened during
fuel vapor storing operations so that air, stripped of fuel vapor
after having passed through the canister, can be pushed out to the
atmosphere. Likewise, during purging operations (for example,
during canister regeneration and while the engine is running), the
vent valve may be opened to allow a flow of fresh air to strip the
fuel vapors stored in the canister. In some examples, canister 22
may include a partition 111 that may extend between the vent 27 and
a vapor canister purge line 28 and conduit 31 to facilitate
distribution of fuel vapor and fresh air throughout the
canister.
[0021] Hybrid vehicle system 6 may have reduced engine operation
times due to the vehicle being powered by engine system 8 during
some conditions, and by the energy storage device under other
conditions. While the reduced engine operation times reduce overall
carbon emissions from the vehicle, they may also lead to
insufficient or incomplete purging of fuel vapors from the
vehicle's emission control system. In some embodiments, to address
this issue, an additional vacuum blocking valve (VBV) 110 (also
referred to as a vapor blocking valve) may be optionally included
in conduit 31 between fuel tank 20 and canister 22. In some
embodiments, VBV 110 may be a solenoid valve wherein operation of
the valve is regulated by adjusting a driving signal (or pulse
width) of the dedicated solenoid.
[0022] During regular engine operation, VBV 110 may be kept closed
to limit the amount of diurnal vapors directed to canister 22 from
fuel tank 20. During refueling operations, and selected purging
conditions, VBV may be opened to direct fuel vapors from the fuel
tank 20 to canister 22. In addition, by opening the VBV during
conditions when the fuel tank pressure is higher than a threshold
(e.g., above a mechanical pressure limit of the fuel tank above
which the fuel tank and other fuel system components may incur
mechanical damage), the refueling vapors may be released into the
canister and the fuel tank pressure may be maintained below
pressure limits. However, opening the VBV under conditions when the
fuel tank pressure is higher than a threshold results in
discontinuous tank pressure release and may lead to sudden
increases in the richness of the purge system effluent which may
impact the purge rate. An alternative to opening the VBV upon a
fuel tank pressure build is to incorporate a restricted vapor
passage around the VBV, thus allowing fuel vapors to slowly and
continuously bleed around the VBV. Adding a small leak path
bypassing 110 reduces or eliminates the need for opening 110 due to
over-pressurization. For example, a restricted vapor line is
commonly incorporated around the VBV such that the fuel tank is
coupled to the load/purge side of the vapor canister (not shown).
Alternately this passage can be implemented via putting a nick (or
notch) into the valve seat of the VBV.
[0023] However, as discussed in further detail below and in
relation to FIGS. 2-3, without line 104 significant fuel tank
vacuum may develop responsive to high purge flow rates in fuel
systems wherein a restricted vapor passage bypasses the VBV. Thus,
according to embodiments disclosed herein, an overall bifurcated
fuel vapor line may be present to couple the fuel tank to both the
fresh air side (107) and load/purge side of the canister (109). The
first segment of the fuel vapor line (104) may include a
restriction (105) and may be coupled to the fresh air side, and not
the load/purge side (109), while the VBV may be disposed in a
second segment of the fuel vapor line coupled to the load/purge
side. Additionally, the restriction disposed in the first vapor
line may comprise a smaller cross-section that the cross section of
the vapor line comprising the VBV under conditions wherein the VBV
is open. In other words, opening the VBV may create a path of least
resistance from the fuel tank to the load/purge side of the vapor
canister.
[0024] Accordingly, as shown in FIG. 1, a first fuel vapor line 104
may contain a restriction 105, in order to limit flow rate, for
example the restriction may comprise an appropriately sized
orifice, sonic choke, etc. First fuel vapor line 104 thus may
function to prevent the tank from pressurizing and tank air and
vapor may come out continuously. In one example, first fuel vapor
line 104 may be fluidically coupled to conduit 31 at a location
upstream of the VBV, between the VBV and the fuel tank, and
fluidically connected to the fresh air side 107 of the vapor
canister. When arranged in this way, fuel vapors from the fuel tank
20 may flow to the vapor canister, via one of two paths, depending
on the state of the VBV. For example, if the VBV is open, fuel
vapors may be directed to the vapor canister via conduit 31 through
open VBV to the load/purge side 109 of the canister. If however,
the VBV is closed, fuel vapors may be directed to the vapor
canister via the first fuel vapor line 104, to the fresh air side
107 of the canister, and not to the load/purge side 109 of the
canister. Incorporation of the fuel vapor line 104, having a
restriction, fluidically coupled to the vapor canister on the fresh
air side may significantly reduce the development of fuel tank
vacuum responsive to high purge flow rates, described in further
detail below and in relation to FIGS. 2-3.
[0025] One or more pressure sensors 120 may be coupled to fuel tank
20 for estimating a fuel tank pressure or vacuum level. For
example, pressure sensor 120 may comprise a fuel tank pressure
transducer (FTPT). While the depicted example shows pressure sensor
120 coupled between the fuel tank and VBV 110 along conduit 31, in
alternate embodiments, the pressure sensor may be coupled to fuel
tank 20. In still other embodiments, a first pressure sensor may be
positioned upstream of the vapor blocking valve, while a second
pressure sensor is positioned downstream of the vapor blocking
valve, to provide an estimate of a pressure difference across the
valve.
[0026] Fuel vapors released from canister 22, for example during a
purging operation, may be directed into engine intake manifold 44
via purge line 28. The flow of vapors along purge line 28 may be
selectively regulated by one or more canister purge valves 106 and
112, coupled between the fuel vapor canister and the engine intake.
In some examples, canister purge valves 106 and 112 may be arranged
in parallel. Canister purge valve 106 may be a conventional
canister purge valve and may comprise a continuously adjustable
valve with a smaller flow cross-section than canister purge valve
112. Accordingly, canister purge valve 112 may be referred to as a
low restriction valve (e.g., having a lower restriction that valve
106), with a larger cross-section than canister purge valve 106. In
some examples, the low restriction valve 112 may comprise a valve
which may be either open or closed, while the purge valve 106, may
be continuously adjusted or regulated. In this way, use of the
adjustable valve may be selectively utilized through a certain
range of engine performance characteristics for a sufficiently fine
control of the purging operation, and only when, for example, a
short, complete purging of the vapor canister is required, may the
second valve be additionally opened. In other examples, only the
canister purge valve 106 or only canister purge valve 112 may be
utilized. As such, responsive to the shorter purge times available
in hybrid vehicles, higher purge flow rates may be thus achieved
via the incorporation of a low restriction valve such as valve 112,
in addition to a conventional purge valve, such as valve 106.
[0027] The quantity and rate of vapors released by the canister
purge valve(s) may be determined by the duty cycle of an associated
canister purge valve solenoid (not shown). As such, the duty cycle
of the canister purge valve solenoid(s) may be determined by the
vehicle's powertrain control module (PCM), such as controller 12,
responsive to engine operating conditions, including, for example,
engine air flow rate, an air-fuel ratio, a canister load, fuel
vapor concentration in the canister effluent, etc. By commanding
the canister purge valve(s) to be closed, the controller may seal
the fuel vapor recovery system from the engine intake.
[0028] Especially for boosted engines, an optional canister check
valve (not shown) may be included in purge line 28 to prevent
intake manifold pressure from flowing gases in the opposite
direction of the purge flow. As such, the check valve may be
necessary if the canister purge valve control is not accurately
timed or the canister purge valve itself can be forced open by a
high intake manifold pressure. An estimate of the manifold absolute
pressure (MAP) may be obtained from MAP sensor 118 coupled to
intake manifold 44, and communicated with controller 12.
Alternatively, MAP may be inferred from alternate engine operating
conditions, such as mass air flow (MAF), as measured by a MAF
sensor (not shown) coupled to the intake manifold.
[0029] Fuel system 18 may be operated by controller 12 in a
plurality of modes by selective adjustment of the various valves
and solenoids. For example, the fuel system may be operated in a
fuel vapor storage mode, wherein the controller 12 may close VBV
110 and open canister vent valve (CVV) 114 while closing canister
purge valve (CPV) 112 to direct vapors into the fresh air side 107
via vapor line 104 to canister 22 while preventing fuel vapors from
being directed into the intake manifold. As such, pressure build-up
in the tank may be avoided and fuel tank vapors effectively
contained within canister 22.
[0030] As another example, the fuel system may be operated in a
refueling mode (e.g., when fuel tank refueling is requested by a
vehicle operator), wherein the controller 12 may open VBV 110 and
canister vent valve 114, while maintaining canister purge valve 112
closed, to depressurize the fuel tank before allowing enabling fuel
to be added therein. As such, VBV 110 may be kept open during the
refueling operation to allow refueling vapors to be stored in the
canister. As the vapor line 104 contains a restriction 105, when
VBV 110 is opened vapors may be directed to the load/purge side 109
of canister 22, as the path of least resistance to vapor flow is
via the conduit 31 to the canister load/purge side. Accordingly,
under conditions wherein vapor generation is high, such as
refueling, vapors are introduced to the canister at the load/purge
side thereby maximizing the exposure of hydrocarbons to adsorbent
material as vapors travel from the load/purge side towards the
fresh air side 107 of canister 22. After refueling is completed,
the VBV and the canister vent valve may be closed.
[0031] As yet another example, the fuel system may be operated in a
canister purging mode (e.g., after an emission control device
light-off temperature has been attained and with the engine
running), wherein the controller 12 may open canister purge valve
112 and canister vent valve 114 sequentially, with the canister
purge valve opened before the canister vent valve is opened.
Herein, the vacuum generated by the intake manifold of the
operating engine may be used to draw fresh air through vent 27 and
through fuel vapor canister 22 to purge the stored fuel vapors into
intake manifold 44. To isolate the fuel tank from the engine intake
manifold vacuum, canister purging may be performed with VBV 110
closed. In this mode, the purged fuel vapors from the canister are
combusted in the engine. The purging may be continued until the
stored fuel vapor amount in the canister (herein also referred to
as the canister load) is below a threshold. During purging, the
learned vapor amount/concentration can be used to determine the
amount of fuel vapors stored in the canister, and then during a
later portion of the purging operation (when the canister is
sufficiently purged or empty), the learned vapor
amount/concentration can be used to estimate a loading state of the
fuel vapor canister. For example, one or more oxygen sensors (not
shown) may be coupled to the canister 22 (e.g., downstream of the
canister), or positioned in the engine intake and/or engine
exhaust, to provide an estimate of a canister load (that is, an
amount of fuel vapors stored in the canister). Based on the
canister load, and further based on engine operating conditions,
such as engine speed-load conditions, a purge flow rate may be
determined.
[0032] As described above, high purge rates may be required
responsive to the shorter purge times available in hybrid vehicles.
High purge rates may be accomplished, for example, via the
incorporation of a low restriction canister purge valve, such as
canister purge valve 112. However, as discussed, high purge flow
rates may result in putting the fuel tank at significant vacuum,
potentially overcoming the fuel tank relief valve 102 thus leading
to the drawing of air and dirt particles into the tank, the air
flow additionally not serving to purge the canister. To meet the
requirement for high purge flow rates and reduced fuel tank vacuum,
a vapor line, such as vapor line 104 may be coupled to the vapor
canister at the fresh air side, and not at the load/purge side. As
such, the vacuum seen by the fuel tank may be far shallower than in
an alternative arrangement in which a vapor line (not shown) is
coupled to the fuel tank on the load/purge side of the vapor
canister.
[0033] Controller 12 may also be configured to intermittently
perform leak detection routines on fuel system 18 to confirm that
the fuel system is not degraded. As such, leak detection routines
may be performed while the engine is off (engine-off leak test) or
while the engine is running (engine-on leak test). Leak tests
performed while the engine is running may include applying a
negative pressure on the fuel system for a duration (e.g., until a
target fuel tank vacuum is reached) and then seal the fuel system
while monitoring a change in fuel tank pressure (e.g., a rate of
change in the vacuum level, or a final pressure value).
[0034] In one example, to perform the leak test, negative pressure
generated at engine intake 23 is applied on the fuel system until a
threshold level is reached. Then, the fuel system is isolated from
the engine intake and a rate of vacuum bleed-up is monitored. Based
on the rate of change in fuel system vacuum, a fuel system leak can
be identified. In another example, where at least some negative
pressure is held in the fuel system (such as at the fuel tank)
before purging is stopped (via timed closing of the canister vent
valve), the fuel system vacuum may be advantageously used during
non-purging conditions to identify a fuel system leak.
Specifically, the fuel tank vacuum/pressure may be monitored during
the non-purging conditions and a leak may be determined based on
the rate at which the fuel tank pressure bleeds up from the vacuum
conditions to barometric pressure. In one example, a fuel system
leak may be determined based on the rate of change in fuel tank
pressure being larger than a threshold rate. Herein, by using the
existing fuel tank vacuum to assess for leaks during non-purging
conditions, the need for an auxiliary or dedicated vacuum source
for performing leak detection routines is decreased. In addition,
by performing the leak detection using the existing fuel system
vacuum during non-purging conditions, completion of the leak
detection routine in the limited engine running time available on
hybrid vehicles may be better enabled.
[0035] VBV 110 may be maintained open during the leak detection
routine. Alternatively, in an example wherein the VBV may be sealed
very tightly when in a closed conformation, the leak detection
routine may be performed with the VBV in both an open and closed
position, thereby narrowing the location of the leak source.
Returning to FIG. 1, vehicle system 6 may further include control
system 14. Control system 14 is shown receiving information from a
plurality of sensors 16 (various examples of which are described
herein) and sending control signals to a plurality of actuators 81
(various examples of which are described herein). As one example,
sensors 16 may include exhaust gas sensor 126 located upstream of
the emission control device, temperature sensor 128, and pressure
sensor 129. Other sensors such as additional pressure, temperature,
air/fuel ratio, and composition sensors may be coupled to various
locations in the vehicle system 6. As another example, the
actuators may include fuel injector 66, VBV 110, purge valves 106
and 112, vent valve 114, and throttle 62. The control system 14 may
include a controller 12. The controller may receive input data from
the various sensors, process the input data, and trigger the
actuators in response to the processed input data based on
instruction or code programmed therein corresponding to one or more
routines. An example control routine is described herein with
regard to FIG. 2.
[0036] In this way, the system of FIG. 1 enables a method for a
fuel system in a hybrid vehicle, to manage fuel vapors during
engine-off conditions including refueling operations, and engine-on
conditions including purging operations. By coupling a vapor line
from the fuel tank to the fresh air side of the vapor canister, the
system of FIG. 1 enables high purge flow rates while protecting the
fuel tank from significant vacuum.
[0037] A flow chart for an example method 200 for managing fuel
vapors is shown in FIG. 2. More specifically, method 200 includes,
in a first condition, for example a canister purging operation,
commanding or maintaining closed a VBV and directing vapor flow
from a fuel tank to a vapor canister via a first vapor line
connecting the fuel tank to a fresh air side of the vapor canister,
not the load/purge side of the canister, and during a second
condition, for example a refueling event, commanding or maintaining
open the VBV and directing flow from the fuel tank to the vapor
canister via a second vapor line connecting the fuel tank to a
load/purge side of the vapor canister. Method 200 will be described
with reference to the system described herein and shown in FIG. 1,
though it should be understood that similar methods may be applied
to other systems without departing from the scope of this
disclosure. Method 200 may be carried out by a controller, such as
controller 12 in FIG. 1, and may be stored at the controller as
executable instructions in non-transitory memory. Instructions for
carrying out method 200 and the rest of the methods included herein
may be executed by a controller based on instructions stored on a
memory of the controller and in conjunction with signals received
from sensors of the engine system, such as the sensors described
above with reference to FIG. 1. The controller may employ engine
actuators of the engine system to adjust engine operation,
according to the method described below.
[0038] Method 200 begins at 205 and includes evaluating current
operating conditions. Operating conditions may be estimated,
measured, and/or inferred, and may include one or more vehicle
conditions, such as vehicle speed, vehicle location, etc., various
engine conditions, such as engine status, engine load, engine
speed, A/F ratio, etc., various fuel system conditions, such as
fuel level, fuel type, fuel temperature, etc., various evaporative
emissions system conditions, such as fuel vapor canister load, fuel
tank pressure, etc., as well as various ambient conditions, such as
ambient temperature, humidity, barometric pressure, etc. At 210
method 200 includes determining whether an engine-off condition is
detected. An engine-off condition may be indicated by a key-off
event, a user setting a vehicle alarm following exiting a vehicle
that has been parked, a user depressing a button, an automatic
engine shutdown, or other suitable indicator. In some examples,
certain vehicle-on, engine-off conditions, such as those which may
occur in a hybrid vehicle operating in battery-only mode, may be
sufficient to proceed with an evaporative emissions system leak
test. If at 210 an engine-off event is detected, method 200
proceeds to 215 where it is determined whether a refueling event
has been requested. For example, a refueling request may comprise a
vehicle operator depression of a refueling button on a vehicle
instrument panel in the vehicle, or at a refueling door. In some
examples, a refueling request may comprise a refueling operator
requesting access to a fuel filler neck, for example, by attempting
to open a refueling door, and/or attempting to remove a gas cap. If
a refueling event has not been requested, the method 200 proceeds
to 220, wherein method 200 includes maintaining the VBV closed.
Maintaining the VBV closed directs any fuel vapors generated while
the engine is off, to the fresh air side of the vapor canister via
the vapor line, such as vapor line 104 described in FIG. 1. As the
vapor line comprises a restriction, such as restriction 105
described in FIG. 1, fuel vapor may be released slowly from the
fuel tank as pressure builds in the fuel tank. In this way,
excessive pressure builds in the fuel tank are avoided, and vapor
released from the fuel tank is efficiently captured in the vapor
canister. Continuing at 230, method 200 includes maintaining the
status of the fuel system, and may further include maintaining the
status of the evaporative emissions system. For example, components
such as the CVV, CPV, and refueling lock may be signaled by the
controller to maintain their current conformation. Method 200 may
then end.
[0039] Returning to 215, if a request for refueling is received,
method 200 proceeds to 235. At 235, method 200 includes
depressurizing the fuel tank. Alternatively, depressurizing the
fuel tank may be conducted at engine-off or key-off at 210. As
described in relation to FIG. 1, a vapor line, such as vapor line
104, may allow excessive pressure builds in the fuel tank to be
avoided by directing fuel tank vapor to the fresh air side of the
canister while the VBV is closed. However, the vapor line may
contain a restriction, such as restriction 105, and as such
pressure in the fuel tank may rise to levels greater than
atmospheric pressure depending on environmental conditions. Thus,
prior to refueling, the fuel tank may be depressurized. For
example, the controller 12 may open a VBV valve (such as VBV 110)
and open or maintain open a vent path between the fuel vapor
canister and atmosphere (e.g., open CVV such as CVV 114), while
maintaining a canister purge valve (e.g., CPV 112) closed, to
depressurize the fuel tank before allowing enabling fuel to be
added therein. The VBV may be opened in a manner to depressurize
the fuel tank at a predetermined rate, so as to prevent rapid
depressurization which may cause damage to fuel system components.
A refueling lock may be maintained locked until the fuel tank
pressure decreases to a threshold pressure (e.g., atmospheric
pressure), and then commanded to unlock, thus allowing access to
the fuel filler neck only following fuel tank depressurization.
[0040] Continuing at 240, method 200 includes maintaining open the
VBV and canister vent path for the duration of the refueling event,
thus directing fuel vapor from the fuel tank to the load/purge side
of the fuel vapor canister, and to allow gasses stripped of
refueling vapors to be flowed to atmosphere. As the flow path from
the fuel tank to the load/purge side comprises the path of least
restriction for the fuel vapor due to the larger cross sectional
area of the vapor line with an open VBV as compared to the
restricted vapor line, vapor flow via the restricted vapor line
(e.g., 104) to the fresh air side of the canister, may be
significantly prevented. The refueling event may be monitored, for
example, via a fuel tank fill level sensor (e.g., 101) and one or
more fuel tank pressure sensors (e.g., 120) for the duration of the
refueling event. Monitoring fuel tank pressure may include
receiving signals from the one or more fuel tank pressure sensors
continuously, or at predetermined time intervals such that a
predetermined number of fuel tank pressure measurements can be
performed over the duration of the refueling event. Similarly,
monitoring fuel level may include the control system receiving
information regarding the level of fuel stored in the fuel tank via
one or more fuel level sensors, either continuously or at
predetermined intervals over the duration of the refueling event.
The end of the refueling event may be indicated based on one or
more of the fuel tank pressure and fuel level. For example, the end
of the refueling event may be indicated when a fuel level has
plateaued for a duration, and when a fuel tank pressure has not
increased over the plateau duration. In other examples, the end of
the refueling event may be indicated responsive to a refueling
nozzle being removed from the fuel filler neck, replacement of a
fuel cap, closing of a refueling door, etc. Continuing at 245,
method 200 includes closing the VBV. With the VBV closed, the path
of least resistance to air flow may thus be via the restricted
vapor line, such as vapor line 104 in FIG. 1. As previously
discussed, due to a restriction (e.g., 105), fuel vapor may be
released slowly, enabling efficient capture of hydrocarbons at the
fresh air side of the vapor canister, and effectively avoiding
excessive fuel tank pressure builds. Following closing the VBV,
method 200 includes updating a canister purge schedule in
accordance with the refueling event and may further include
updating a canister loading state. A canister loading state may be
determined based on hydrocarbon sensors, and/or temperature sensors
positioned within the vapor canister, fuel tank pressure during the
refueling event, etc. In another example, closing the VBV may be
delayed until shortly after engine startup. Method 200 may then
end.
[0041] Returning to 210, if an engine-off event is not detected,
method 200 proceeds to 255 where it is determined whether purge
conditions are met. In one example, purge conditions may be
considered met when the canister load (estimated or inferred) is
higher than a threshold. The canister load may be estimated based
on, for example, pressure differences across the canister, an
air/fuel ratio estimated downstream of the canister, hydrocarbon
sensors and/or temperature sensors positioned within the vapor
canister, and/or based on fuel vapor concentrations learned on an
immediately previous canister loading and/or purging operation. If
at 255 it is determined that purge conditions are not met, method
200 proceeds to 260 where the VBV is maintained closed. As such,
maintaining the VBV closed directs fuel vapors from the fuel tank
to the fresh air side of the vapor canister, not the load/purge
side, via the restricted vapor line, such as vapor line 104. Thus,
during engine on conditions, pressure builds in the fuel tank due
to, for example increases in temperature as a result of engine
operation, may be released via the restricted vapor line and vapors
captured and stored in the vapor canister. Continuing at 265,
method 200 includes maintaining current engine operating
conditions. For example, components such as the CVV, CPV may be
signaled by the controller to maintain their current conformation.
Method 200 may then end.
[0042] Returning to 255, if it is determined that purge conditions
are met, method 200 proceeds to 270. At 270, method 200 includes
maintaining closed the VBV. Maintaining closed the VBV during a
purge operation ensures that fuel vapor will not be drawn out of
the fuel tank by intake manifold vacuum. Next, at 275, method 200
includes opening one or more canister purge valves, for example
canister purge valves 106 and 112 as described in FIG. 1. In one
example, requirement for a low purge flow rate may be indicated
based on canister purge conditions specified at 255, thus only a
low flow canister purge valve, such as purge valve 106, may be
opened and/or adjusted. In other examples, requirement for a high
canister purge flow rate may be indicated based on canister purge
conditions specified at 255. Responsive to a high canister purge
rate requirement, both low flow canister purge valve (e.g., 106)
and high flow/low restriction purge valve (e.g., 112) may be opened
and/or adjusted.
[0043] Continuing at 280, method 200 includes purging hydrocarbons
from a fuel system canister to an engine intake with the CVV and
the one or more canister purge valves open, and with the VBV
maintained closed. More specifically, by opening the one or more
canister purge valves, an intake manifold vacuum (from the running
engine) is applied on the canister bed and hydrocarbons stored in
the canister are drawn into, and combusted in, the engine. With the
CVV open, fresh air is concomitantly forced to flow through the
canister bed, increasing the efficiency of the canister purge. As
discussed above, if high flow purge rates are required, excessive
fuel tank vacuum may result under some conditions. More
specifically, a high flow rate through the canister creates a
pressure drop across the canister, the pressure drop equating to a
vacuum at the canister line coupled to the CPVs (106, 112), i.e.,
at 103. Because the fuel tank conduit 31 couples to the vapor
canister in the same region, the fuel tank sees the same vacuum.
This may be corrected by coupling the fuel tank to the fresh air
side of the vapor canister, not the load/purge side, via the
restricted vapor line (e.g., 104), and adding VBV 110. Thus, the
VBV blocks the vacuum to the tank while line 104 vents the tank to
a pressure near atmosphere. In an example wherein a leak orifice is
included within VBV 110, orifice 105 may be significantly larger
than the leak orifice within 110, thereby maintaining the fuel tank
nearer atmospheric pressure than the vacuum at 103. In this way,
high canister purge flow rates may be achieved without excessive
fuel tank vacuum generation, even in the presence of an intended
leak flow through a closed VBV 110.
[0044] To ensure excessive vacuum does not develop, at 275, method
200 includes indicating whether there is negative pressure in the
fuel tank, and if the fuel tank vacuum is greater than a threshold.
At 285, indicating whether fuel tank vacuum is greater than a
threshold may include receiving signals from one or more fuel tank
pressure sensors, such as fuel tank pressure sensor 120,
continuously, or at predetermined time intervals over the duration
of the purging operation. If at 285, it is determined that fuel
tank vacuum is greater than a threshold, method 200 proceeds to
290. At 290, method 200 includes adjusting purge flow. In one
example, adjusting purge flow may include adjusting the low flow
canister purge valve (e.g., 106) to a more closed state, such that
the overall purge flow rate is reduced and a reduction in fuel tank
vacuum is achieved. In another example, the high flow/low
restriction canister purge valve (e.g. 112) may be commanded shut,
thus reducing purge flow to a level determined by the state of the
low flow canister purge valve. Other examples of adjusting purge
flow via exerting control over the one or more canister purge
valves may additionally be contemplated.
[0045] Returning to 285, if it is determined that fuel tank vacuum
is not greater than a threshold, or alternatively if fuel tank
vacuum is greater than a threshold requiring purge flow adjustment
at 290, method 200 proceeds to 292 where it is determined if the
canister load (estimated or inferred) is lower than a threshold.
More specifically, it may be determined if the canister has been
sufficiently purged such that the purging operation can be
discontinued. Canister loading state may be determined based on
hydrocarbon sensors, and/or temperature sensors positioned within
the vapor canister, for example. If the canister load is not below
a threshold, the routine may return to 270 to continue purging
hydrocarbons from the canister. If sufficient canister purging has
occurred, then method 200 includes closing the CPV at 294. Method
200 then proceeds to 296 where a canister purge schedule is
updated. For example updating the canister purge schedule may
include updating the loading state of the canister. Method 200 may
then end.
[0046] FIG. 3 shows an example timeline 300 for conducting a vapor
canister purge operation according to the methods described herein
and with reference to FIG. 2, and as applied to the systems
described herein and with reference to FIG. 1. Timeline 300
includes plot 310, indicating a canister load, over time. Line 315
represents a first threshold canister load, above which indicates
that a canister purge operation is required. Line 320 represents a
second threshold canister load, below which represents a purged
canister. Timeline 300 further includes plot 325, indicating the
open or closed state of a canister purge valve over time, plot 330,
indicating the open or closed state of a canister vent valve over
time, and plot 335, indicating the open or closed state of a vapor
blocking valve over time. Timeline 300 further includes plot 340,
indicating whether a refueling event is occurring, over time.
Timeline 300 further includes plot 345, indicating the off or on
state of the engine, over time. Timeline 300 further includes plot
350, indicating the pressure in the fuel tank, over time. Line 355
represents a threshold vacuum, below which the level of vacuum is
such that air may be drawn into the tank via a fuel tank relief
valve.
[0047] At time t.sub.0, the engine is off, indicated by plot 345,
and is in a state of being refueled, indicated by plot 340. As
such, the VBV, indicated by plot 335, and the CVV, indicated by
plot 330, are both open. Additionally, the CPV, indicated by plot
325, is closed. As described further in relation to FIG. 1, when
the VBV is open the path of least resistance to vapor flow from the
fuel tank to the canister is via the vapor line (e.g., 31) to the
canister load/purge side, not to the fresh air side. Accordingly,
during refueling, wherein vapor generation is high, the
introduction of vapors to the load/purge side serves to maximize
the exposure of hydrocarbons to the adsorbent material housed
within the canister, as vapors travel from the load/purge side
towards the fresh air side of the canister. As the vehicle is being
refueled, fuel tank pressure is slightly above atmospheric
pressure, indicated by plot 350.
[0048] As such, between time t.sub.0 and t.sub.1, during the course
of the refueling event, canister load increases, indicated by plot
310. As described above, canister load may be estimated based on,
for example, pressure differences across the canister, an air/fuel
ratio estimated downstream of the canister, hydrocarbon sensors
and/or temperature sensors positioned within the vapor canister,
and/or based on fuel vapor concentrations learned on an immediately
previous canister loading and/or purging operation. At time
t.sub.1, the refueling even is complete. Accordingly, the VBV is
commanded closed. With the VBV closed, the fuel system may be
operating in a storage mode wherein fuel vapors are directed to the
fresh air side (e.g., 107), not the load/purge side (e.g., 109), of
the vapor canister via the restricted vapor line (e.g., 104). As
such, pressure build-up in the tank may be avoided and fuel tank
vapors effectively contained within the canister.
[0049] At time t.sub.2, the engine is turned on. Between time
t.sub.2 and t.sub.3, while the vehicle is in operation, the
canister load continues to slightly build as a result of heat
transfer from the engine to the fuel tank. With the VBV closed,
vapors generated in the fuel tank are directed to the canister via
the restricted vapor line (e.g., 104). At time t.sub.3, canister
load crosses a threshold, indicated by line 315, indicating a
requirement for a purge operation. The threshold may be set based
on, for example, a load state such that further introduction of
fuel vapor to the canister may result in bleed emissions. Based on
the canister load reaching a threshold, a high purge flow rate may
be indicated. Accordingly, to achieve a high flow rate, one or more
of canister purge valve(s) (e.g., 106, 112) are commanded open,
indicated by plot 325. As one example, both a low flow (e.g., 106)
and a high flow (e.g., 112) canister purge valve may be commanded
open. Additionally, the CVV, indicated by plot 330 is maintained
open, and the VBV, indicated by plot 335 is maintained closed.
[0050] Between time t.sub.3 and t.sub.4, the vapor canister is
purged by high flow. Accordingly, the canister load state steadily
decreases during the purging operation, indicated by plot 310.
Additionally, fuel tank vacuum is monitored by a fuel tank pressure
sensor (e.g., FTPT 120). As the canister is being purged with a
high flow, the fuel tank experiences the development of a vacuum,
yet the vacuum does not reach a threshold vacuum, indicated by line
355. The threshold may indicate a vacuum sufficient to draw air
(and dirt) in via the fuel tank vacuum relief valve (e.g. 102).
That the fuel tank vacuum remains below a threshold results from
the arrangement of the restricted vapor line (e.g., 104) described
in relation to FIG. 1 and the method described in FIG. 2. With the
VBV closed during purge operation and the restricted vapor line
coupled to the fuel tank and the fresh air side of the vapor
canister, high purge flow rates are enabled while avoiding the
development of excessive fuel tank vacuum.
[0051] At time t.sub.4 canister load crosses a threshold, indicated
by line 320. Accordingly, the canister has been sufficiently purged
and thus the CPV is commanded closed. As the engine is still in
operation, the CVV is maintained open, and the VBV is maintained
closed. During the time between t.sub.4 and t.sub.5, the canister
load state begins to increase, the result of heat transfer from the
engine to the fuel tank, thus generating fuel vapors that are
directed from the fuel tank to the fresh air side, not the
load/purge side, of the canister.
[0052] In this way, fuel tank vapors may be directed to a fuel
vapor canister via one or more of a plurality of pathways, based on
the open or closed state of a VBV. For example, vapors may be
directed to a fresh air side, and not a load/purge side, of the
fuel vapor canister in the case where the VBV is closed, and
directed toward a load/purge side, and not a fresh air side, of the
canister when the VBV is opened. As such, during a refueling event
when vapor generation is at a high level, VBV may be in an open
state, thus fuel tank vapors may be directed towards a load/purge
side of the vapor canister, maximizing the potential for vapor
adsorption via the vapor canister. In another example, during a
canister purge event, the VBV may be commanded closed, thus
preventing the flow of fuel vapors from the fuel tank to the
engine. In yet another example, including an engine-off condition
wherein the vehicle is not in a refueling operation, the VBV may be
closed, thus fuel tank vapors may be directed towards the fresh air
side of the vapor canister, preventing the fuel tank from
pressurizing and capturing fuel tank vapors in the vapor
canister.
[0053] The technical effect directing fuel tank vapors to a fuel
vapor canister via one or more of a plurality of pathways, based on
the open or closed state of a VBV is to preserve the functionality
of the VBV and restricted vapor line arrangement, while reducing
the amount of fuel tank vacuum generated during purging operations.
In this way, due to the shorter purge times available in hybrid
vehicles, the purge operations may comprise much higher rates while
excessive fuel tank vacuum may be avoided. By enabling higher vapor
canister purge rates, the vapor canister may be more effectively
purged of stored hydrocarbons, thus reducing evaporative
emissions.
[0054] The systems described herein and with reference to FIG. 1,
along with the methods described herein and with reference to FIG.
2 may enable one or more systems and one or more methods. In one
example, a method for an engine, comprises, during a first
condition, closing a vacuum blocking valve (VBV) and directing
vapor flow from a fuel tank to a fresh air side of a vapor canister
via a first vapor line; and during a second condition, opening the
VBV and directing vapor flow from the fuel tank to a load/purge
side of the vapor canister via a second vapor line. In a first
example of the method, the method includes wherein directing vapor
flow via the first vapor line comprises directing vapor flow
through a restriction in the first vapor line. A second example of
the method optionally includes the first example and further
includes wherein the restriction is comprised of an orifice or a
sonic choke. A third example of the method optionally includes any
one or more or each of the first and second examples and further
includes wherein an overall vapor line bifurcates upstream of the
restriction into the first vapor line and second vapor line,
wherein the VBV is positioned in the second vapor line. A fourth
example of the method optionally includes any one or more or each
of the first through third examples and further includes wherein
the first condition comprises engine operation. A fifth example of
the method optionally includes any one or more or each of the first
through fourth examples and further includes wherein the first
vapor line does not couple the fuel tank to the load/purge side of
the vapor canister. A sixth example of the method optionally
includes any one or more or each of the first through fifth
examples and further includes wherein the first condition comprises
a canister purge event. A seventh example of the method optionally
includes any one or more or each of the first through sixth
examples and further includes wherein the vapor canister is divided
into the fresh air side and the load side by a partition housed
within the canister, the fresh air side further including a vent
line connected to fresh air via a canister vent valve (CVV), the
load side connected to an intake manifold via one or more canister
purge valves (CPV), including a conventional CPV and/or a low
restriction CPV. An eighth example of the method optionally
includes any one or more or each of the first through seventh
examples and further comprises, during the canister purge event,
commanding open the low restriction CPV. A ninth example of the
method optionally includes any one or more or each of the first
through eighth examples and further includes wherein the canister
purge event comprising an open low restriction CPV includes
indicating whether a fuel tank vacuum is greater than a threshold.
A tenth example of the method optionally includes any one or more
or each of the first through ninth examples and further includes
wherein indicating a fuel tank vacuum greater than a threshold
includes reducing purge flow rate such that fuel tank vacuum is
maintained below the threshold. An eleventh example of the method
optionally includes any one or more or each of the first through
tenth examples of the method and further includes wherein the
second condition includes a refueling event.
[0055] An example of a system for an engine comprises a fuel vapor
canister partitioned into a fresh air side and a load/purge side; a
fuel tank; and a bifurcated vapor line connecting the vapor
canister to the fuel tank, a first segment of the line comprising a
restricted orifice disposed within the first vapor line segment and
connecting to the vapor canister on the fresh air side, a second
segment of the vapor line comprising a vacuum blocking valve (VBV)
disposed within the second vapor line segment and connecting to the
vapor canister on the load/purge side. In a first example, the
system further comprises a canister vent line coupled to the fuel
vapor canister on the fresh air side; a canister vent valve
disposed within the canister vent line and configured to
selectively couple the vapor canister to fresh air; a canister
purge line coupled to the fuel vapor canister on the load/purge
side; and one or more canister purge valves (CPV) disposed within
the canister purge line and configured to selectively couple the
vapor canister to the an intake manifold. A second example of the
system optionally includes the first example and further comprises
a controller holding executable instructions stored in
non-transitory memory, that when executed, cause the controller to:
during engine operation, command the VBV closed; and during a
refueling event, command the VBV open. A third example of the
system optionally includes any one or more or each of the first and
second examples and further includes wherein the one or more CPVs
comprise a first CPV and a second, low restriction CPV having a
lower restriction than the first CPV, and wherein the controller
has further instructions that when executed cause the controller
to, during a canister purge event, open the low restriction CPV and
maintain the VBV closed. A fourth example of the system optionally
includes any one or more or each of the first through third
examples and further includes wherein when the VBV is open, the
second segment of the bifurcated vapor line has a smaller amount of
restriction than the first segment of the bifurcated vapor line
such that fuel vapor may flow from the fuel tank to the vapor
canister load side via the open VBV.
[0056] Another example of a system for an engine comprises a fuel
vapor canister partitioned into a fresh air side and a load/purge
side; a fuel tank; and a bifurcated vapor line connecting the vapor
canister to the fuel tank, a first segment of the vapor line
comprising a restricted orifice disposed within the first vapor
line segment and connecting to the vapor canister on the fresh air
side, a second segment of the vapor line comprising a vacuum
blocking valve (VBV) disposed within the second vapor line segment
and connecting to the vapor canister on the load/purge side; a
canister vent line coupled to the fuel vapor canister on the fresh
air side; a canister vent valve disposed within the canister vent
line and configured to selectively couple the vapor canister to
fresh air; a canister purge line coupled to the fuel vapor canister
on the load/purge side; a first canister purge valve (CPV) and
second CPV each configured to selectively couple the vapor canister
to the an intake manifold, the second CPV having a lower
restriction than the first CPV; and a controller holding executable
instructions stored in non-transitory memory, that when executed,
cause the controller to: responsive to a request to perform a
canister purge with a target flow rate above a threshold, maintain
the VBV closed, open the second CPV, and adjust a position of the
first CPV to reach the target flow rate, and responsive to a
request to refuel the fuel tank, open the VBV. In a first example,
the system further comprises wherein the second segment of the fuel
vapor line has a cross-sectional area that is larger than a
cross-sectional area of the orifice, and wherein when open, the VBV
does not restrict the second segment of the fuel vapor line. A
second example of the system optionally includes the first example
and further includes wherein the first segment of the vapor line
does not couple the fuel tank to the load/purge side of the vapor
canister, and wherein the second segment of the vapor line does not
couple the fuel tank to the fresh air side of the vapor
canister.
[0057] Note that the example control and estimation routines
included herein can be used with various engine and/or vehicle
system configurations. The control methods and routines disclosed
herein may be stored as executable instructions in non-transitory
memory and may be carried out by the control system including the
controller in combination with the various sensors, actuators, and
other engine hardware. The specific routines described herein may
represent one or more of any number of processing strategies such
as event-driven, interrupt-driven, multi-tasking, multi-threading,
and the like. As such, various actions, operations, and/or
functions illustrated may be performed in the sequence illustrated,
in parallel, or in some cases omitted. Likewise, the order of
processing is not necessarily required to achieve the features and
advantages of the example embodiments described herein, but is
provided for ease of illustration and description. One or more of
the illustrated actions, operations and/or functions may be
repeatedly performed depending on the particular strategy being
used. Further, the described actions, operations and/or functions
may graphically represent code to be programmed into non-transitory
memory of the computer readable storage medium in the engine
control system, where the described actions are carried out by
executing the instructions in a system including the various engine
hardware components in combination with the electronic
controller.
[0058] It will be appreciated that the configurations and routines
disclosed herein are exemplary in nature, and that these specific
embodiments are not to be considered in a limiting sense, because
numerous variations are possible. For example, the above technology
can be applied to V-6, I-4, I-6, V-12, opposed 4, and other engine
types. The subject matter of the present disclosure includes all
novel and non-obvious combinations and sub-combinations of the
various systems and configurations, and other features, functions,
and/or properties disclosed herein.
[0059] The following claims particularly point out certain
combinations and sub-combinations regarded as novel and
non-obvious. These claims may refer to "an" element or "a first"
element or the equivalent thereof. Such claims should be understood
to include incorporation of one or more such elements, neither
requiring nor excluding two or more such elements. Other
combinations and sub-combinations of the disclosed features,
functions, elements, and/or properties may be claimed through
amendment of the present claims or through presentation of new
claims in this or a related application. Such claims, whether
broader, narrower, equal, or different in scope to the original
claims, also are regarded as included within the subject matter of
the present disclosure.
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